In many types of sports equipment, such as baseball, hockey and lacrosse, for instance, the handle portion thereof is usually made of a hard, smooth material such as wood or aluminum consequently, the handle becomes slippery when in the course of the game moisture from the hands of the user coats the handle surface.
Friction tape which makes use of a porous cloth which is permeated by adhesive has commonly been used by athletes. This characteristic stickiness gives the handle an unpleasant feel and furthermore does little to cushion the hands against shocks resulting from the contact of the sports equipment with the object to be hit.
Furthermore, it has been found difficult in practice to decrease the overall weight of sports equipment since it would lead to weaker and less stiff equipment thereby resulting in breakage and lower performance standards.
It should also be noted that a baseball bat made of wood, for instance, has a relatively small “sweet zone” where the contact of the baseball with the bat will result in maximum energy transfer.
Baseball bats have traditionally been made of wood. Today, wood baseball bats are all made of heavy and strong hardwoods, primarily ash. Ash (or other similar hardwoods such as hickory or birch) baseball bats result in bats where the rule of thumb is the length in inches equals the weight in ounces. Thus, today's wood baseball bats limit bat speed and also, are prone to catastrophic breakage. Such catastrophic breakage could lead to injury of not only players but also to bystanders and are a real concern to authorities. Also, as wood bats dry out (i.e. loose moisture), they lose strength and breakage increases.
The following is a comparison of the densities of various types of hardwoods and softwoods based on weight when oven dry and volume at 12% moisture content, taken from data contained in the Wood Handbook—Wood as an Engineering Material, published in 1999 by Forest Products Society of Madison, Wis.:
HardwoodDensity lb/ft3Hickory, true Mockernut50.3Yellow Birch43.3White Ash41.9Paper Birch39.1Yellow Poplar29.4Aspen Bigtooth27.3Aspen Quaking26.6
SoftwoodDensity lb/ft3Fir Balsam24.5Cottonwood-Balsam poplar23.8Balsa11.2
Density of wood is generally proportional to strength and stiffness. For example yellow poplar is 30% lighter than white ash with a corresponding decrease in strength. Hardwoods are both stronger and stiffer than softwoods and, most importantly, they are more impact resistant than softwoods. Only hardwoods have the required strength and impact resistance for the applicant's baseball bats.
More recently, aluminum baseball bats have captured a large majority market share versus wood bats, even though they are more expensive and players complain about vibrations and the “pinging” sound when a baseball is hit. There are two reasons for the aluminum bat's success: 1) they are lighter than wood baseball bats, thus increasing bat speed and increasing hitting distance, and 2) they are less prone to breakage than wood bats.
Most recently, in an attempt to further lower weights of aluminum bats, thinner walled aluminum bats have been produced; however, problems have been encountered with balls leaving depressions in the bat and also, bat breakage.
U.S. Pat. No. 4,014,542, which issued to Tanikawa on Mar. 29, 1977, describes a five component baseball bat having a softwood balsam core, a main member made of foam, a metal tube having apertures for bonding fixed to the barrel portion only of the main member, and an outer layer of glass fibre which is painted with a synthetic resin. Even though Tanikawa's bat is durable and is designed to reduce the shock caused by contact with a baseball, Tanikawa does not improve hitting performance by reducing the weight of the bat when compared to a conventional bat, while at the same time enhancing bat strength and stiffness. Moreover, the construction of Tanikawa's bat is not a “structural sandwich” which combines a single strong thin composite outer layer with a thick lightweight core to reduce the overall weight of the bat while at the same time enhancing bat strength, stiffness and durability.
U.S. Pat. No. 5,458,330, which issued to Baum on Oct. 17, 1995, describes a multi-component bat having between five and eleven layers. Baum's bat includes external layers of wood veneer over a plurality of resin impregnated fabric socks, which in turn surround inner cores of foam, wood or aluminum which may include cavities. Baum's bat is designed to have the appearance of a conventional wood bat with the objective of being less susceptible to breakage and comparable in performance. Baum, however, does not improve hitting performance by reducing the weight of the bat when compared to a conventional bat, while at the same time enhancing bat strength and stiffness. Neither does the construction of Baum's bat comprise a “structural sandwich” for reducing weight while maintaining or enhancing bat strength, durability and performance.
The following is a specific properties chart showing the density, stiffness and strength properties of various possible materials for use in making baseball bats. All data is taken from standard text books available in the field. Specific stiffness and specific strength are actual stiffness and strength divided by density respectively. Strengths for composite materials are given as tensile strength measured along fiber direction in a unidirectional part. Strength for wood is given as the minimum of tensile and compressive ultimate strength. Strength for metal is given as ultimate tensile strength. Densities of white ash, yellow poplar and bigtooth aspen are taken from the above table of wood densities:
DensityStiffnessSpecificStrengthSpecificMaterialslbs/ft3M/SIStiffnessK/SIStrengthSteel AISI 30448730.003.9085.0010.90Aluminum 6061-T616910.003.7045.0016.60Aluminum 7075-T616910.003.7083.0030.50Titanium Ti-75A28317.003.7080.0017.70High Modulus10238.0023.30165.00100.00GraphiteIntermediate10234.0019.50180.00109.80Modulus GraphiteCommercial9821.0013.30210.00132.90GraphiteE-Glass13017.003.10135.0064.30S-Glass1248.004.00155.0077.60Kevlar 498611.008.00210.00152.20White Ash422.003.008.0012.10Bigtooth Aspen271.002.304.009.30Yellow Poplar291.102.404.509.80
Polymer composites are over 16 times stronger than ash and 60% stronger than aluminum. However, they are over three times heavier than ash while approximately 20% lighter than aluminum, those being hollow therefore lighter than solid composite bats, on an equal volume basis. In summary, an all polymer composite baseball bat would be much stronger than either an ash or aluminum bat, but would be much too heavy.
By careful selection and combination of materials of varying densities, strengths and stiffness, such as those listed above, the applicant has been able to achieve weights for various baseball bat models (for example softball, youth, baseball, etc.) that are lower than traditionally constructed bats and that, at the same time, have improved mechanical properties, such as strength, stiffness and durability, and thus improved performance.
The performance, durability and appearance of sports equipments can be dramatically improved by construction of such equipments, with lighter cores over-wrapped by polymer composite.
We shall discuss the applicant's composite over-wrapped lightweight core through its application to a baseball bat but it is understood that it applies to other sports equipment and tool handles as well if applicable.